Scientists have found that
drought played a key role, but the Mayans appear to have
exacerbated the problem by cutting down the jungle canopy to make
way for cities and crops, according to researchers who used
climate-model simulations to see how much deforestation
aggravated the drought.

"We're not saying deforestation explains the entire drought, but
it does explain a substantial portion of the overall drying that
is thought to have occurred," said the study's lead author
Benjamin Cook, a climate modeler at
Columbia University's Lamont-Doherty Earth Observatory and the
NASA Goddard Institute for Space Studies, in a
statement. [Dry
and Dying: Images of Drought]

Using climate-model simulations, he and his colleagues examined
how much the switch from forest to crops, such as corn, would
alter climate. Their results, detailed online in the journal
Geophysical Research Letters, suggested that when
deforestation was at its maximum, it could account for up to
60 percent of the drying. (The switch from trees to corn reduces
the amount of water transferred from the soil to the atmosphere,
which reduces rainfall.)

Other recent research takes a more holistic view.

"The ninth-century collapse and abandonment of the Central Maya
Lowlands in the Yucatán peninsular region were the result of
complex human–environment interactions," writes this team in a
study published Monday (Aug 20) in the journal Proceedings of the
National Academy of Sciences.

The team, led by B.L. Turner, a social scientist at Arizona State
University, concurs that by clearing the forest, the Mayans may
have aggravated a natural drought, which spiked about the time
the empire came to an end and population declined dramatically.

But this is just one contributing factor to their demise, Turner
and colleagues write, pointing out that the reconfiguration of
the landscape may also have led to soil degradation. Other
archaeological evidence points to a landscape under stress, for
instance, the wood of the sapodilla tree, favored as construction
beams, was no longer used at the
Tikal and Calakmul sites beginning in A.D. 741. Larger
mammals, such as white-tailed deer, appear to have declined at
the end of empire.

Social and economic dynamics also contributed. Trade routes
shifted from land transit across the Yucatán Peninsula to
sea-born ships. This change may have weakened the city states,
which were contending with environmental changes. Faced with
mounting challenges, the ruling elites, a very small portion of
the population, were no longer capable of delivering what was
expected of them, and conflict increased.

"The old political and economic structure dominated by
semidivine rulers decayed," the team writes. "Peasants,
artisan – craftsmen, and others apparently abandoned their homes
and cities to find better economic opportunities elsewhere in the
Maya area."